The present invention relates to a button switch, and more particularly to the button switch in which a rubber piece having a plurality of thin metal wires embedded therein and electrically conductive films applied to both surfaces to constitute a key button contact portion is provided on a lower face of a pushing member of the button switch.
As shown in FIG. 6, a conventional button switch has been composed of a key button 61, a contact portion 62 provided on a lower face of a pushing member of this key button 61, and contact patterns 64 printed and wired on a printed circuit board 63. Usually, the key button 61 is made of silicone rubber 65 or the like as shown in FIG. 7, and an electrically conductive film 66 made of carbon or the like as the contact portion has been bonded to a lower face of the pushing member of the key button made of the silicone rubber 65.
In the conventional key button switch provided with the contact portion employing the carbon contact or so, in case where the printed circuit board etc. acting as a portion to be contacted is free from foreign substances such as dust, oil, or flux of solder, etc. as shown in FIG. 8, normal switching operation can be performed by pushing the pushing member of the key button. However, in case where the foreign substances such as dust, oil, or flux of solder, etc. have been adhered to the portion to be contacted such as the printed circuit board as shown in FIG. 9, the contacts become inconductive, resulting in a problem of defective switching operation of the switch.